Multi-pass spectroscopy apparatus, associated sample holder and methods

ABSTRACT

A sample cell includes an annular support surrounding a sample region. A set of reflectors of the annular support define an optical path that reflects a source beam in a sequence of alternating directions through the sample region at a plurality of different angles such that the source beam exits the set of reflectors after having passed through the sample region a plurality of times. A micro-cell is positionable in the sample region including multi-dimensionally distributed nano-pores. A slidingly adjustable lens forms part of source and detector photomixing packages.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under program 1831168awarded by the National Science Foundation. The Government has certainrights in this invention.

BACKGROUND

The present invention is generally related to the field of spectroscopyand, more particularly, to a multi-pass spectroscopy apparatus, packagesfor coupling radiation into and from a semiconductor device, sampleholder and related methods.

Figure la is a block diagram of a photomixing spectrometer system,generally indicated by the reference number 10, and configured inaccordance with the prior art. It is noted that such a system can beemployed for terahertz (THz) radiation production and detection. System10 has been presented for purposes of providing a framework for thediscussion of problems which can arise in the prior art, but which arenot limited to the field of spectroscopy. System 10 includes a firstlaser 12 and a second laser 14 which are optically coupled to a fiberoptic 2×2 optical coupler 16 through optical fibers 18 and 20,respectively. A first output 24 is optically coupled to a sourcephotomixer 30 through an optical fiber 34 and to a detector photomixer38 through an optical fiber 40. The source and detector photomixers arepositioned relative to a sampling region 50 in which a sample material52 is positioned. Detector photomixer 38 is electrically connected to adetection circuit 54 through an electrical cable 58.

First laser 12 and second laser 14 can be semiconductor diode lasers,such as distributed feedback (DFB) lasers, that each produce opticalradiation at a different single frequency from one another at any giventime. The first laser can generate a first optical radiation 60 and thesecond laser can generate a second optical radiation 64, wherein theoptical radiation is represented using arrows. The optical frequency ofthe light from either one or both of the lasers can be controlled bychanging the temperature of one or both of the lasers; and thedifference between the optical frequencies is in the frequency range of1 kHz to over 5 THz. Fiber optic coupler 16 receives optical radiation60 and 64 from the lasers and optically outputs a combined opticalradiation 70 on both outputs that is made up of optical radiation 60 and64. The source and detector photomixers can be low-temperature grownGaAs photo conductive mixers. The source and detector photomixersreceive combined optical power 70 and optically photomix the opticalradiation from the two lasers to produce and detect THz radiation,respectively. The source photomixer includes a biased antenna (notshown), and the mixing of the optical radiation on the biased antenna ofthe source photomixer generates a THz beam 74 that is radiated towardsample region 50. The mixing of the optical radiation on the detectorphotomixer, which is unbiased, provides a local oscillator required forhomodyne detection. The THz radiation generated by the source photomixercan be swept through a range of frequencies by changing the frequencydifference between the optical frequencies. The THz beam is directedfrom the source photomixer through sample region 50 in which the beaminteracts with material 52 before traveling to detector photomixer 38 asa modified THz energy subject to interaction with sample 52. In thedetector photomixer, modified THz radiation 80 is mixed with the localTHz radiation generated by mixing combined optical radiation (i.e., thelocal oscillator) 70 and is down-converted to an electrical signal 84(shown as an arrow). The detector signal is supplied to detectioncircuit 54 over electrical cable 58. The detection circuit receives thedetector signal and produces a response that can be used to generate anoutput that is characterized by the presence of sample material 52. Theterahertz frequencies applied to the sample material in the presentembodiment can be in a range from about 50 GHz to 3 THz.

Still referring to Figure la, Applicant recognizes that the amount ofinfluence that sample material 52 has on THz beam 74 can be verylimited, given that the beam passes through the sample material only onetime. Generally, the prior art has attempted to address this problem byincreasing the thickness of the sample. Applicant recognizes that thisis of limited value, if the molecule of interest resides in a highlyabsorbent compound, since increasing the thickness will result incomplete absorption of the beam and obfuscation of the molecularinteraction with the beam. For example, many molecules of biologicalimportance need to be measured while in an aqueous solution. However,water is extremely absorbent and therefore makes characterizingbiological compounds very difficult. Simply increasing the path lengthwithout somehow removing the water will result in a complete loss ofsignal.

FIG. 1b illustrates an embodiment of a standard photomixer package thatcan be incorporated into prior art system 10, generally indicated by thereference number 82 and diagrammatically shown in an elevational view.The basic structure that is shown can serve as either source photomixer30 and/or detector photomixer 38 of FIG. 1 a. For purposes of brevity,the use of this structure as source photomixer 30 will be described.Optical power 83 is received, for example, from optical fiber 34 andfocused onto a photomixer chip 85 which itself is fixedly attached to asilicon lens 86. THz radiation 87, for example, can be produced by chip85, collected by lens 86 and externally emitted by the lens. Applicantrecognizes that there are at least two significant issues with thisarchitecture. The first issue is that the center of photomixer chip 85must be aligned very precisely with the center of lens 86. If thephotomixer is offset, the THz beam leaving the photomixer is directed ata corresponding angle a from a centerline 88 of silicon lens 86.Relaxing the positional tolerance on the placement of the photomixeressentially means that any instrument employing photomixers requires asecond lens 90 or a mirror (not shown) to correct pointing variationfrom device to device to a desired direction 91. The second issue thatApplicant recognizes concerns an impact on device versatility andproduction. Because photomixer chip 85 is sitting against a frontsurface 92 of silicon lens 86, the choice of lens is required at thetime of device manufacture and cannot subsequently be changed. In thisregard, Applicant recognizes that it is not uncommon for a device enduser to request an optical system that focuses output beam 91 instead ofcollimating the beam. This can lead to the need for a custom packagingrun, which can be costly and time consuming.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods which aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

In general, embodiments and methods are described relating to a samplecell for use as part of a spectrometer including a source whichgenerates a source beam that includes electromagnetic radiation forcharacterizing a sample that is within a sample region. In an embodimentof the sample cell, an annular support surrounds the sample region forreceiving the source beam along an entrance path such that the sourcebeam initially passes through the sample region and the sample containedin the sample region. A set of reflectors is supported by the annularsupport to define an optical path that reflects the source beam, afterinitially passing through the sample region, in a sequence ofalternating directions through the sample region at a plurality ofdifferent angles such that the source beam exits the set of reflectorsafter having passed through the sample region and any sample containedtherein a plurality of times.

In another aspect of the present disclosure, embodiments of an apparatusand associated methods are described in relation to a spectrometerincluding a source which generates a source beam that includeselectromagnetic energy for characterizing a sample that is supported ina sample region. The apparatus includes a micro-cell having an outerperiphery including a length extending between a first end and a secondend such that an interior portion of the micro-cell serves as the sampleregion, and the micro-cell defines a plurality of nano-pores forreceiving the sample, each nano-pore having an elongated dimensionextending at least generally along a direction of the length and thenano-pores are distributed along two orthogonal dimensions transverse tothe length.

In another aspect of the present disclosure, embodiments of an apparatusand associated methods are described in relation to a spectrometerincluding a source which generates a source beam that includeselectromagnetic energy for characterizing a sample that is supported ina sample region. The apparatus includes an annular support surroundingthe sample region for receiving the source beam along an entrance pathsuch the source beam initially passes through the sample region and thesample contained in the sample region. A set of reflectors is supportedby the annular support to define an optical path that reflects thesource beam, after initially passing through the sample region, in asequence of alternating directions through the sample region and at aplurality of different angles such that the source beam exits the set ofreflectors after having passed through the sample region and any samplecontained therein a plurality of times. A micro-cell is supported withinthe sample region, the micro-cell having an outer periphery confrontingthe set of reflectors and the outer periphery includes a lengthextending between a first end and a second end such that an interiorportion of the sample cell serves as the sample region by receiving thesample within a plurality of nano-pores, each nano-pore having anelongated dimension extending at least generally along a direction ofthe length and the nano-pores are distributed along two orthogonaldimensions transverse to the length.

In another aspect of the present disclosure, an assembly and associatedmethods are described in which a port is supported for accepting anoptical power. A semiconductor device is supported for receiving theoptical power from the port and mixing the optical power to produce anemitted radiation. A window includes first and second opposing majorsurfaces with a thickness therebetween and the window is fixedlysupported adjacent to the semiconductor device to place the firstopposing major surface in a confronting relationship with thesemiconductor device for receiving the emitted radiation and the secondopposing major surface is outwardly facing with respect to thesemiconductor device such that the emitted radiation passes through thewindow and exits from the second opposing major surface. A lens is atleast initially selectively positionable on the second, outwardly facingmajor surface of the window for selective alignment with thesemiconductor device through the window based on sliding engagementbetween an input surface of the lens and the second opposing majorsurface of the window such that the emitted radiation enters the lensfrom the window and an angular orientation of the emitted radiationexiting from the lens is adjustable responsive to sliding engagement ofthe lens on the window which changes the selective alignment.

In another aspect of the present disclosure, an assembly and associatedmethods are described in which a semiconductor device is supported forreceiving electromagnetic radiation and generating an electrical signalbased on the electromagnetic radiation. A window includes first andsecond opposing major surfaces with a thickness therebetween and thewindow is fixedly supported adjacent to the semiconductor device toplace the first opposing major surface in a confronting relationshipwith the semiconductor device with the second opposing major surfaceoutwardly facing with respect to the semiconductor device. A lens is atleast initially selectively positionable on the second, outwardly facingmajor surface of the window for selective alignment with thesemiconductor device through the window based on sliding engagementbetween a planar surface of the lens and the second opposing majorsurface wherein the electromagnetic radiation is captured by the lens atan angular orientation that is adjustable responsive to slidingengagement of the lens on the window which changes the selectivealignment and, thereafter, the optical power passes through the windowto the semiconductor device.

In another aspect of the present disclosure, an assembly and associatedmethods are described in which a semiconductor device is supported forreceiving electromagnetic radiation and generating an electrical signalbased on the electromagnetic radiation. The assembly includes a portthat is supported for accepting an optical power. A semiconductor deviceis supported for receiving the optical power from the port and mixingthe optical power to produce an emitted radiation. A window having firstand second opposing major surfaces with a thickness therebetween isfixedly supported adjacent to the semiconductor device to place thefirst opposing major surface in a confronting relationship with thesemiconductor device for receiving the emitted radiation and the secondopposing major surface is outwardly facing with respect to thesemiconductor device. The emitted radiation passes through the windowand exits from the second opposing major surface. A lens is at leastinitially selectively positionable on the second, outwardly facing majorsurface of the window for selective alignment with the semiconductordevice through the window based on sliding engagement between an inputsurface of the lens and the second opposing major surface of the windowsuch that the emitted radiation enters the lens from the window and anangular orientation of the emitted radiation exiting from the lens isadjustable responsive to sliding engagement of the lens on the windowwhich changes the selective alignment.

In a continuing aspect of the present disclosure, an assembly andassociated methods are described in which a semiconductor device issupported for receiving electromagnetic radiation and generating anelectrical signal based on the electromagnetic radiation. The assemblyincludes a semiconductor device that is supported for receivingelectromagnetic radiation and generating an electrical signal based onthe electromagnetic radiation. A window having first and second opposingmajor surfaces with a thickness therebetween is fixedly supportedadjacent to the semiconductor device to place the first opposing majorsurface in a confronting relationship with the semiconductor device andthe second opposing major surface is outwardly facing with respect tothe semiconductor device such that a lens is at least initiallyselectively positionable on the second, outwardly facing major surfaceof the window for selective alignment with the semiconductor devicethrough the window based on sliding engagement between a planar surfaceof the lens and the second opposing major surface, wherein theelectromagnetic radiation is captured by the lens at an angularorientation that is adjustable responsive to sliding engagement of thelens on the window which changes the selective alignment and,thereafter, the optical power passes through the window to thesemiconductor device.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Example embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be illustrative rather than limiting.

FIG. 1a is a block diagram of a prior art photomixing spectrometersystem.

FIG. 1b is a diagrammatic view of a prior art photomixing package thatcan be used in the photomixing spectrometer system of FIG. 1 a.

FIG. 2 is a block diagram of an embodiment of a sample analysis system,diagrammatically showing a multi-pass sampling apparatus configured inaccordance with the present disclosure.

FIG. 3 is a further enlarged diagrammatic view of the multi-passsampling apparatus of FIG. 2, shown here to illustrate further detailsof its structure and operation.

FIG. 4 is a diagrammatic view, in perspective, illustrating furtherdetails of an embodiment of the multi-pass sampling apparatus of FIGS. 2and 3.

FIG. 5 is a diagrammatic illustration of an embodiment of a modifiedsystem that includes a modified multi-pass sampling apparatus inaccordance with the present disclosure.

FIG. 6 is a diagrammatic illustration of another embodiment of amodified system which includes a dual multi-pass sampling apparatus inaccordance with the present disclosure.

FIG. 7 is a diagrammatic view, in perspective, illustrating anembodiment of a multi-path mirror ring surrounding an embodiment of amicro-cell, each of which is produced in accordance with the presentdisclosure.

FIG. 8 is a further enlarged, diagrammatic view, in perspective,illustrating the embodiment of the micro-cell shown in FIG. 7.

FIGS. 9 and 10 are diagrammatic, fragmentary views, in perspective,shown here to illustrate embodiments of a micro-cell having concavefacets and convex facets, respectively, in accordance with the presentdisclosure.

FIG. 11 is a diagrammatic illustration, in a perspective view, of anembodiment of a micro-cell produced in accordance with the presentdisclosure.

FIG. 12 is a further enlarged diagrammatic, fragmentary view of aportion of the top/end surface of the nano-fluidic cell of FIG. 11,illustrating the potential appearance of individual nano-pores.

FIGS. 13a and 13b diagrammatically illustrate, in perspective views, theproduction and structure of another embodiment of a nano-fluidic cell inaccordance with the present disclosure.

FIG. 13c is a diagrammatic, fragmentary and further enlarged view of aportion of an end face of an embodiment of a photonic rod that is shownin FIG. 13b , in accordance with the present disclosure.

FIGS. 14a and 14b diagrammatically illustrate the production andstructure for still another embodiment of a nano-fluidic cell inaccordance with the present disclosure.

FIG. 15 is an elevational diagrammatic, cut-away view of an embodimentof a nano-fluidic cell, in which a sample is sealed within nano-pores inaccordance with the present disclosure.

FIG. 16 is an elevational diagrammatic, cut-away view of an embodimentof a nano-fluidic cell, in which a sample flows through nano-pores inaccordance with the present disclosure.

FIGS. 17 and 18 illustrate diagrammatic views, in elevation, of aphotomixing package produced in accordance with the present disclosureand its associated operation.

FIG. 19 is a diagrammatic plan view of a modified photomixing packagebased on the photomixing package of FIGS. 17 and 18.

DETAILED DESCRIPTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention and is provided in the contextof a patent application and its requirements. Various modifications tothe described embodiments will be readily apparent to those skilled inthe art and the generic principles taught herein may be applied to otherembodiments. Thus, the present invention is not intended to be limitedto the embodiment shown, but is to be accorded the widest scopeconsistent with the principles and features described herein includingmodifications and equivalents, as defined within the scope of theappended claims. It is noted that the drawings are not to scale and arediagrammatic in nature in a way that is thought to best illustratefeatures of interest. Descriptive terminology may be used with respectto these descriptions, however, this terminology has been adopted withthe intent of facilitating the reader's understanding and is notintended as being limiting. Further, the figures are not to scale forpurposes of illustrative clarity.

FIG. 2 is a block diagram of an embodiment of a sample analysis system,generally indicated by the reference number 100, and configured inaccordance with the present disclosure. In the present embodiment aspectrometry system is shown, although this is not intended to belimiting based on the discussions that follow. To the extent that thecomponents of system 100 reflect the features of system 10, describedabove, descriptions of like components may not be repeated for purposesof brevity and like reference numbers may be applied. A source 104 and adetector 108 can be, by way of non-limiting example, photomixers,photoconductive switches (PCSs), diodes or any suitable component eithercurrently available or yet to be developed, that mixes combined opticalradiation 70 at two different wavelengths to generate a differencefrequency. The source and detector photomixers are generally arrangedside-by-side such that the source generates a source (i.e., pre-sample)radiation 110, which may be referred to as a source beam, and thedetector receives a post-sample radiation 114, both of which areillustrated by arrows. In the present embodiment, the source photomixercan generate source radiation 110 as THz energy, based on a bias, whilethe detector photomixer can be unbiased. THz radiation generated by thesource photomixer can be swept through a range of frequencies bychanging a frequency difference between the optical frequencies.

Still referring to FIG. 2, detector 108 is electrically coupled to asensitive current detection circuit that is made up of an amplifier 120that is coupled to a lock-in amplifier 124 which provides an output to acomputer 128 that can generate results 130. The lock-in amplifier alsoreceives an input from a reference oscillator 134 that generates a lowfrequency reference signal which is also supplied to a bias amplifier140. The bias amplifier provides an AC bias at a reference frequency tosource photomixer 104. Amplifier 120 increases the signal level fromdetector photomixer 108 and feeds the signal into lock-in amplifier 124.Computer 128 records the output from the lock-in amplifier 124 anddisplays output 130 as a function of time or frequency.

The components of system 100 described thus far can be thought of as asample interrogation system 200 to the left of a dashed vertical line204 in the view of the figure. The objective of sample interrogationsystem 200 is to generate source, pre-sample radiation 110 and detectpost-sample radiation 114. It is noted that, while sample interrogationsystem 200 illustrates a frequency domain spectroscopy system, this isnot a requirement. In this regard, a time domain system can be used assample interrogation system 200 with equal applicability. To the rightof line 204, system 100 further includes a multi-pass samplingapparatus, an embodiment of which is illustrated, as produced inaccordance with the present disclosure, diagrammatically shown in a planview and generally indicated by the reference number 210. As will beappreciated, based on the discussions that follow, multi-pass samplingapparatus 210 of the present disclosure can be utilized in any systemthat is capable of generating source (i.e., pre-sample) radiation 110and then detecting post-sample radiation 114 for analysis purposes andis not limited, for example, to spectroscopy.

Multi-pass sampling apparatus 210 of FIG. 2 includes an annular support230 that defines an inner periphery 234 surrounding a sample region 240that is illustrated as a dashed circle centered within annual support230. In the present embodiment, the inner periphery is at leastgenerally circular, although any suitable shape can be used. The annularsupport can be formed from any suitable materials including, but notlimited to aluminum and in any suitable manner such as, for example, bymachining. In the present embodiment, the annular support is a frameworkthat defines an aperture or opening 244 for receiving source beam 110therethrough and for allowing post-sample radiation 114 to travel todetector 108. In another embodiment, a partition 246 can be providedsuch that an exit aperture is provided separate from an entranceaperture. The source beam travels to sample region 240 to be incidentupon a sample carrier or holder or 250 and a sample 254 that issupported by the sample carrier. It is noted that the sample holder canbe employed for holding liquids, solids, corrosive gasses or othercompounds that should not interact with the interior of the samplechamber and/or annular support as well as related components, yet to bedescribed.

Annular support 230 is configured to support a plurality of mirrors 260around inner periphery 234. In combination, annular support 230 andmirrors 260 may be referred to as a multi-path mirror ring 262. Mirrors260 are configured to cooperate as pairs with an example pair of mirrors264 shown within a dashed ellipse. In the present embodiment, there are18 mirror pairs, although any suitable number can be used. As will beseen, a first mirror 268 of each pair initially receives radiation 270that has traveled through sample region 240 and sample holder 250. Thefirst mirror then reflects the radiation as intermediate radiation 272to a second mirror 273 of the pair which then directs the radiation backto the center of the sample region as focused radiation 274. Focusedradiation 274 then travels through the sample region and sample 254 aspost-sample radiation 276 that has traveled through the sample two timesto a second pair of mirrors 278. Reflection then continues step-wise inalternating directions through the sample and around the periphery ofthe annular support in this manner to form an overall multi-pass beampath, described immediately hereinafter.

Referring to FIG. 3 in conjunction with FIG. 2, the former illustratessystem 100 in a diagrammatic plan view with the addition of a beam path280 that is propagated by the mirror pairs around the inner periphery ofthe annular support while sample interrogation apparatus 200 ispartially shown as it interfaces with multi-pass sampling apparatus 210.It is noted that the mirror pairs are numbered in accordance with thesequence in which the path alternates across the sample region whilestepping around the inner periphery of the annular support until aneighteenth mirror pair 284 directs the beam path through the sample todetector 108 as post-sample radiation 114 for detection. For purposes ofclarity, arrowheads have been applied to segments of beam path 280between the mirror pairs and the sample to show the direction of travelalong each segment. Accordingly, pre-sample radiation 110 afterinitially passing through the sample region, travels in a sequence ofalternating directions through the sample region at a plurality ofdifferent angles such that the source beam emerges as post-sampleradiation 114 from aperture 244 (FIG. 2) of the annular support on apath segment 282 after having passed through the sample region and anysample contained therein a plurality of times. In this embodiment, it isnoted that pre-sample radiation 110 and post-sample radiation 114 enterand exit, respectively, through a shared aperture in annular support230. As is evident based on the shape of the beam path in FIG. 3, themirrors of each mirror pair cooperate to focus post-sample radiationinto sample holder 250 (FIG. 2) which then diverges after travelingthrough the sample region. In order to accomplish this, at least onemirror 268 or 273 of each mirror pair performs focusing as the radiationpropagates. One suitable type of mirror for performing focusing, by wayof a non-limiting example, is a toroidal mirror. In one embodiment,mirror 268 can be a flat mirror while mirror 273 is a focusing mirror.In another embodiment, mirror 268 can be a focusing mirror while mirror273 is a flat mirror. In still another embodiment, both mirrors 268 and273 can be focusing mirrors. Any suitable material can be used to formthe mirrors including, but not limited to aluminum. It is noted that alens can be provided, if needed, to focus pre-sample radiation 110 fromsource 104 to sample region 240 (FIG. 2). Applicant notes that there isno requirement for the beam path to move stepwise around essentially acomplete circle as shown. That is, in some embodiments, there can be agreater angular offset between source 104 and detector 108 around theannular support such that fewer mirror pairs can be used. In this case,aperture 244 can serve as an entry point for pre-sampling radiation 110and a separate aperture can be provided for post-sampling radiation 114.

Attention is now directed to FIG. 4, which is a diagrammatic view, inperspective, illustrating further details of an embodiment of multi-passsampling apparatus 210 of FIGS. 2 and 3. The reader is referred to thedescriptions above with respect to designated features and components.

FIG. 5 is a diagrammatic illustration of an embodiment of a modifiedsystem 100′ which includes a modified multi-pass sampling apparatus210′. To the extent that system 100′ and multi-pass sampling apparatus210′ share the features of previously described system 100 with respectto sample interrogation system 200 and multi-pass sampling apparatus210, descriptions of such shared features will not be repeated and thereader is referred to the descriptions above. In system 100′, multi-passsampling apparatus 210′ has been modified to include a reflector 300that can be, for example, a mirror or a retro-reflector which reflectsand focuses the post-sample radiation back to sample region 240 suchthat the radiation doubles back in a reverse direction to travel toaperture 244, doubling the length of the path as well as the number oftimes that the radiation travels through the sample. It is noted thatthe mirror pairs reflect the radiation in a reverse order for thereverse direction with respect to the numbering of the mirror pairs. Inthis embodiment, an optical splitter 320 is inserted into a path segment304 as part of modified sample interrogation apparatus 200′ such thatpost-sampling radiation 114 is deflected to detector 108, as shown,while pre-sampling radiation 110 travels from source 104 through theoptical splitter to the sample region. Moreover, as compared to sampleinterrogation apparatus 200 of FIGS. 2 and 3, modified sampleinterrogation apparatus 200′ illustrates source 104 and detector 108rearranged in order to cooperate with the optical splitter. It should beappreciated that optical splitter 320 can be of any suitable type suchas, for example, mylar. It is noted that arrows designating thedirection of travel on individual segments of optical beam path 280 havebeen removed since the travel is bidirectional in this embodiment.

FIG. 6 is a diagrammatic illustration of a modified system 400 whichincludes a dual multi-pass sampling apparatus that is generallyindicated by the reference number 410. To the extent that system 400 anddual multi-pass sampling apparatus 410 share the features of previouslydescribed system 100 of FIGS. 2-4 and system 100′ of FIG. 6,descriptions of shared features will not be repeated and the reader isreferred to the descriptions above. In system 400, modified sampleinterrogation system 200′ of FIG. 5 is used. Further, multi-passsampling apparatus 210 of FIG. 3 is used as a first multi-pass samplingapparatus in conjunction with the introduction of a mirror 414 on asegment 418 that formerly was received by the detector. Instead, asegment 420 bidirectionally extends the beam path to a second multi-passsampling apparatus, which corresponds to modified multi-pass samplingapparatus 210′ of FIG. 5, via a mirror 424. It is noted that mirrors 414and 424 can be off-axis parabolic mirrors. Generally, multi-passsampling apparatus 210 and modified multi-pass sampling apparatus 210′will be used with the same sample material in their respective sampleregions. As compared to multi-pass sampling apparatus 210 of FIG. 3,dual multi-pass sampling apparatus 410 of FIG. 6 provides a path lengththat is four times longer and the beam path passes through the twocombined sample regions four times as many times by connecting twomulti-pass sampling apparatuses in series. It should be appreciated thatany suitable number of such apparatuses can be connected in series inthis manner and is not limited to two. In another embodiment, multi-passsampling apparatus 210 and modified multi-pass sampling apparatus 210′can be arranged in a stacked configuration such that one major side ofapparatus 210 is in a confronting relationship with another major sideof apparatus 210′ rather than in the illustrated side-by-sideconfiguration. In this embodiment, mirrors 414 and 424 can bereoriented, as needed. Further, the sample regions of apparatus 210 and210′ are aligned in this stacked configuration such that the samplematerial can be shared, for example, within an elongated samplecontainer extending between the two sampling apparatuses and configuredin a manner that is consistent with the descriptions that follow.

FIG. 7 is a diagrammatic view, in perspective, illustrating anembodiment of multi-path mirror ring 262 surrounding an embodiment of amicro-cell produced in accordance with the present disclosure, generallyindicated by the reference number 500 and serving as the aforedescribedsample holder 250 of FIG. 2. FIG. 8 is a further enlarged diagrammaticview, in perspective, shown here to illustrate further details ofmicro-cell 500. In the present embodiment, micro-cell 500 includes atubular shell 510 that is at least generally cylindrical and defines aninterior that serves as a sample region 514 for receiving a sample. Itis noted that, in the view of FIG. 7, the upper portion of themicro-cell has been truncated for purposes of clarity to betterillustrate beam paths extending through the micro-cell. Applicantrecognizes that configuring the micro-cell with essentially a perfectlycylindrical surface, such that a cross-sectional shape taken orthogonalto an axis 516 of the cylinder defines a circle, can produce undesiredeffects on propagation in the beam path (see, for example, FIG. 3)produced by multi-path mirror ring 262, since the micro-cell wouldfunction as a cylindrical lens, leading to excessive losses duringpropagation. While mirrors 260 can be designed to compensate for sucheffects of the outer periphery of the micro-cell as well as theperiphery of sample region 514, Applicant recognizes that it isdifficult to modify the mirrors for testing samples with differentoptical properties that can cause effects such as, for example,reflections to vary in an unpredictable way. In order to avoid theseeffects, Applicant configures tubular shell 510 with a faceted periphery520 that is made up of a plurality of side-by-side facets 524, severalof which are individually designated in FIG. 8, that are at leastgenerally parallel to axis 516 of the micro-cell. In an embodiment, thefacets can be flat or planar although any suitable shape can be usedsuch that the energy traveling on the beam path is neither focused nordefocused. The outer periphery transverse to the length of themicro-cell can form a closed polygon having a plurality of sides thatare all adjoined by an obtuse angle. FIG. 7 illustrates an individualbeam path segment 530 that is centered on a facet 532 extending from thecenter of one mirror 534 to a focal point 536 at a center of sampleregion 514. Similarly, an opposing beam path segment 538 is shown inboth FIGS. 7 and 8 in association with a facet 540.

FIGS. 9 and 10 are diagrammatic, fragmentary views, in perspective shownhere to illustrate an embodiment of the micro-cell, generally indicatedby the reference number 550 in FIG. 9, having concave facets 554 andanother embodiment of the micro-cell, generally indicated by thereference number 560 in FIG. 9, having convex facets 564. In anotherembodiment, tubular shell 510 can have a cylindrical outer peripherywithout facets and with mirrors 260 (see, for example, FIGS. 2 and 7)configured as spherical mirrors to complement the performance of thecylindrical shell (operating as a cylindrical lens) to focus beam pathsegments to the center of the sample region.

FIG. 11 is a diagrammatic illustration, in a perspective view, of anembodiment of a micro-cell produced in accordance with the presentdisclosure and generally indicated by the reference number 600. To theextent that the features of micro-cell 600 reflect the features ofmicro-cell 500 of FIGS. 8 and 9, descriptions of such features may notbe repeated for purposes of brevity and the reader is referred to thedescriptions above. In this embodiment, the sample region is configuredas a nano-fluidic cell 604 that includes a plurality of nano-pores 610for receiving a sample therein. FIG. 12 is a further enlargeddiagrammatic, fragmentary view of a portion of the top/end surface ofnano-fluidic cell 604 illustrating the potential appearance ofindividual nano-pores, several of which are designated by the referencenumber 614. The nano-pores comprise voids that have an elongateddimension extending at least generally along a direction that isparallel to axis 516 (FIG. 8) of the length of the micro-cell and arenon-circular transverse to the elongated dimension. Moreover, thenano-pores are distributed along two orthogonal dimensions transverse tothe length of the length of the nano-fluidic cell forming atwo-dimensional shape in the visible, top surface of micro-cell 600.

While the configuration of systems in accordance with the presentdisclosure provide for multipath measurements of a solid material in asample region, embodiments of micro-cell 600 provide for multi-pathmeasurements of DNA and RNA samples within nano-pores 614. In thisregard and by way of non-limiting example, terahertz spectroscopy isable to uniquely identify a range of molecules of interest, but becauseTHz radiation is strongly absorbed by water, its use in characterizationof biological samples has been limited. Applicant recognizes thatnano-pores 614 alleviate issues with respect to the need for an aqueoussolution. In particular, the nano-pores serve to concentrate abiologically important molecule while simultaneously limiting the amountof energy absorbing water. In this regard, nano-pores 614 are somewhattriangular in shape with arcuate sides. The cross sectional area ofsuitable nano-pores can be as small as 100 nm² It is noted that thespecific shape of the nano-pores shown in FIG. 12 is not a requirement,as will be discussed at an appropriate point below. Unlike priorsystems, micro-cell 600 as part of a system configured in accordancewith the teachings herein, provides for multi-path exposure of a samplecontained by the micro-pores to enhance the response of the system tothe sample in a way that is submitted to be heretofore unknown. Forexample, Applicant believes that the response can be enhanced by anorder of magnitude, as compared to conventional systems.

Still referring to FIGS. 11 and 12, an embodiment of micro-cell 600 canbe produced through physically drawing a plurality of elongatedcylindrical members such as, for example, rods and/or tubes. Such rodsand/or tubes can be formed from any suitable material that can be drawnincluding but not limited to quartz, glass, plastic and polymers.Initially, these rods or tubes can be captured by a sheath 630 that ispositioned within tubular shell 510. In the embodiment of FIGS. 11 and12, solid rods can be used such as, by way of non-limiting example,optical fibers. This assembly can then be drawn as a preform under hightemperature in the same manner that optical fibers are formed. Suitablematerials for the rods/tubes and sheath include quartz or glass. It isnoted that a polymer or plastic material may also be drawn in thismanner. Nano-pores 614 form in the gaps between adjacent ones of theelongated members. The dimensions of nano-pores 614 are responsive tothe diameter of the rods that are initially used. A rod end 634 isdiagrammatically shown as a dashed circle in FIG. 12. If tubes are usedhaving a central through opening, rather than rods, it is noted that theopening can close as a result of drawing. In another embodiment,nano-fluidic cell 604 can be formed as a component by drawing a preformwith subsequent insertion into the opening defined by tubular shell 510.The nano-fluidic cell in such an embodiment can be held in position, forexample, by a suitable adhesive such as, for example, epoxy. As will beseen, nano-pores can be formed in a wide variety of ways while remainingwithin the scope of the teachings of the present disclosure.

Applicant recognizes that because dielectrics are transparent in the THzregime, plastic or carbon tubes and/or rods can be employed to form amicro-cell without the need for drawing a preform. In such anembodiment, these tubes and/or rods can be bundled in a sheath materialand/or by using a suitable adhesive. Such tubes and/or rods and can becoated with biologically active molecules to allow selective attachmentto specific molecules. In other embodiments, photonic fibers that definepassages that are sufficiently small so as to serve as nano-pores can bebundled to one another, for example, using a suitable adhesive such as,for example, an epoxy.

FIGS. 13a-13c diagrammatically illustrate the production and structureof another embodiment of a nano-fluidic cell in accordance with thepresent disclosure. FIG. 13a shows a preform, generally indicated by thereference number 700 and in a perspective view. In an embodiment, thematerials that make up this preform can be quartz, although this is nota requirement. Preform 700 includes a core 704 that is a solid rodsurrounded by an annular ring 708 of tubes, several of which areindividually designated by the reference number 710 and each of whichdefines a center through hole. A shell 714 receives core 704 and annularring 708 to capture these components in place for the drawing process.Heat 720, shown as arrows, is applied to draw the preform under theforce of gravity in a well-known manner to form a drawn rod 724. FIG.13b is a diagrammatic view, in perspective, illustrating the structureof a portion 730 of rod 724 proximate to a dashed circle 728 in FIG. 13a. FIG. 13c is a diagrammatic, fragmentary and further enlarged view of aportion of an end face 734 of rod portion 730 of FIG. 13b within adashed circle 738 that is shown in FIG. 13b . In FIG. 13c , an annularring of nano-pores 740 is formed that are circular transverse to theelongated length of rod portion 730. It is noted that additionalnano-pores having essentially the same shape as nano-pores 614 of FIG.12 can be formed, if desired, between rods 710 and dependent upon thediameter of the rods. In instances where these additional nano-pores arenot wanted, a frit material or glass solder can be used in the preformto fill the space that would otherwise define the additional pores. Inorder to complete a micro-cell, rod portion 730 can be received intubular shell 510 (see FIG. 11). In some embodiments, facets can beformed directly on shell 714, for example, during the drawing processthrough an appropriately shaped die to complete a micro-cell without theneed for an additional tubular shell such that a tubular shell isessentially integrally formed. In view of FIGS. 13a -13 c, it should beappreciated that a wide range of structures can be produced. Forexample, the diameter of core 704 can be adjusted to provide for the useof a greater or lesser number of rods, thereby changing the width ofannular ring 740 of nano-pores. In order to control the amount of waterin the micro-cell and as is the case with essentially all micro-cellembodiments, the number of nano-pores can be controlled responsive tosuitable design factors such as, for example, the diameter of the core.In still another embodiment, core 704 can be eliminated such that shell714 is completely filled or packed with tubes 710 or solid rods.

FIGS. 14a and 14b diagrammatically illustrate the production andstructure for still another embodiment of a nano-fluidic cell inaccordance with the present disclosure. FIG. 14a diagrammaticallyillustrates photonic fibers 750 assembled in a group in a perspectiveview. Photonic fibers 750 can include pores 754 that can be severalmicrons in diameter. This bundle of photonic fibers can be bundledtogether in the manner of a preform. In an embodiment, the photonicfiber bundle can be contained within a shell such as, for example, shell714 of FIGS. 13a -13 c. FIG. 14b diagrammatically illustrates theresulting structure after drawing as a photonic fiber rod, generallyindicated by the reference number 780, in a perspective view. An array784 of sub-micron nano-tubes or nano-pores 786 is formed along adirection that is at least generally parallel to an elongated directionof the structure. An outline of one photonic fiber 788 is represented bya dashed circle in FIG. 14b . Of course, frit material or glass soldercan be used as a filler to obtain a desired overall shape, as well as tofill gaps between adjacent photonic fibers In this way, heating anddrawing can form a regular, smooth peripheral shape for insertion, forexample, into tubular shell 510 of FIG. 11 to form a micro-cell. In someembodiments, facets can be formed directly on a periphery 790 of theresulting photonic rod, for example, during the drawing process throughan appropriately shaped die to form a micro-cell without the need for anadditional tubular shell, essentially with the tubular shell integrallyformed.

Attention is now directed to FIG. 15 which illustrates an embodiment inan elevational diagrammatic, cut-away view of a nano-fluidic cell,generally indicated by the reference number 800. In this embodiment,nano-pores 804, a plurality of which are multi-dimensionally distributedand several of which are individually designated, extend along a lengthL of the nano-fluidic cell. In this embodiment, the end openings ofnano-pores 804 are in communication with reservoirs 805 which contain asample 810 therein such that sample 810 is also present in thenano-pores. Depending upon the particular application, electrodes 814can be connected to a bias source 815 to apply an electric field toinduce electrophoresis. Reservoirs 805 can be sealed by electrodes 814or the reservoirs can be sealed separately with the electrodes appliedas a separate component. In another embodiment which does not requirereservoirs 805, sealing of the nano-pore openings can be accomplished inany suitable manner such as, for example, by using electrodes 814 sealedto the body of the nano-fluidic cell in a suitable manner such as, forexample, by a rubber gasket. In still another embodiment, the nano-poreopenings can be sealed by an end plate without utilizing electrodes 814,bias source 815 and reservoirs 805. These various embodimentsdemonstrate that a high degree of flexibility is envisioned for adaptingthe nano-fluidic cell to a particular application. As in all embodimentsof the sample cell described herein, the sample can be any suitablematerial of interest such as, for example, a liquid, a gas and/orparticles of a solid that are suspended. As noted above, the nano-porescan limit the amount of water to which the interrogating energy isexposed, thereby enhancing the system response to the sample ofinterest. Moreover, the sample cell can contain samples that would bedetrimental to the remaining components of the system outside the samplecell, for example, causing corrosion. FIG. 16 illustrates anotherembodiment in an elevational diagrammatic, cut-away view of anano-fluidic cell, generally indicated by the reference number 820. Itis noted that descriptions of common features shared with the embodimentof FIG. 15 will not be repeated for purposes of brevity. In thisembodiment, sample 810 flows through the nano-fluidic cell by enteringan entry port 824 in a direction 828, shown by an arrow, into a firstmanifold 830 that is in communication with the nano-pores and exitingfrom the nano-pores into a second manifold 834 to then exit through anexit port 838 in a direction 840 that is indicated by an arrow. Again,electrodes 814 and power source 815 can be utilized although this is nota requirement. In the embodiment of FIG. 16, the electrodes can includeapertures that are aligned with the nano-pores or the electrodes can beporous. In another embodiment, an electrode material can be supported byor form upper and lower manifolds 830 and 834, respectively.

FIG. 17 is a diagrammatic, cut-away view, in elevation, of a photomixingdevice or package, generally indicated by the reference number 900. Itis noted that device 900 can serve as either a source such as, forexample, source 104 in FIG. 2 or as a detector such as, for example,detector 108 of the same figure. As will be further described, device900 addresses Applicants' recognitions of certain deficiencies that werebrought to light with respect to FIG. 1 b.

Structurally, device 900 of FIG. 17 includes a base assembly 904 thatsupports a photomixer 908 or other suitable semiconductor device on amounting surface 910 through which an electrical interface can be madevia electrical connection pins 912. Photomixer 908 can be in opticalcommunication 914, indicated as a double-headed arrow, with an externalelement. The external element can be optical fiber 34 (FIG. 2), by wayof non-limiting example, on a light path 920 that extends to photomixer908. A window 924 can be fixedly attached to a window mounting surface928 in a suitable manner such as, for example, by using epoxy such thatphotomixer 908 can be in optical communication through the window. Inthis manner, the photomixer can be in direct physical contact with aconfronting major surface of the window. An opposing major surface 930of the window supports a lens 934 that is received in a pocket 938 thatcan be spaced apart from the periphery of the lens. The lens caninclude, for example, a cylindrical periphery 939 surrounding acircular, planar base such that the lens can be moved transversely inany given direction from a centered position. At least initially, lens934 is slidably received against major surface 930 of the window forslidable movement up and down, as indicated by arrows 940a and 940b,respectively, as well as normal to (into and out of) the plane of thefigure. By moving lens 934 laterally with respect to light path 920, thelight path to the left of photomixer 908 can be adjusted, by way ofexample, from a misaligned light path 944, shown using a dashed arrowthat is not aligned with light path 920 to an aligned light path 920′,that aligns with light path 920 through the device. As noted above,misalignment between a fixed lens and photomixer 908 can result inmisaligned light path 944, for example, responsive to mountingtolerances of a fixed lens and/or the photomixer itself. Of course, itshould be appreciated that adjustments can be made to align light path920′ to essentially any desired direction and is not restricted toalignment with light path 920. Subsequent to performing the adjustment,lens 934 can be fixed into an adjusted position in any suitable mannersuch as, for example, by UV cure epoxy.

In FIG. 17, because the wavelength of radiation in device 900 such as,for example, THz radiation can be significantly longer than thepotential gap between major surface 930 of the window and the planarsurface of lens 934, this interface has no significant effect on theperformance of the assembled device. Moreover, attaching lens 934 as asecondary process also allows for (in-the-field) customization, sincethe devices can be manufactured in bulk without installing a lens butwith window 924 installed. In this way, any desired type of lens can beinstalled at a later date post-manufacture. In the present example, lens934 is shown as a convex lens. In other embodiments, this lens can be aconcave lens or a Fresnel lens. Once device 900 is aligned against afar-field reference 950 and locked in place, the need for a secondarylens (see Figure lb) or a mirror for redirection is eliminated. It isnoted that for low temperature applications, where infrared (IR)radiation from the device is unwanted, embodiments can include ahigh-reflectivity optical coating that can be sputtered onto outwardlyfacing surface 930 of the window. This serves to prevent the IR frombeing transmitted along, for example, with THz radiation. The interfacebetween window 924 and lens 934 can also support other coatings ormaterials in other embodiments that may normally be desired, forexample, for a free-space THz beam such as a metal structure forpolarization control or wavelength selectivity. In a particularembodiment, a thin section of Lithium Niobate can act as a THzwave-plate. Incorporating such features into this interface can decreasethe number of external components that would otherwise be needed. It isnoted that lens 924 and window 934 can be formed from any suitablematerial or materials including but not limited to silicon, sapphire,glass and polymer or combinations thereof and based on wavelength(s) ofinterest.

Still referring to FIG. 17 operation of photomixing package or assembly900 will now be described serving as a photomixing source, for example,serving as source 104 in FIG. 2. In this configuration, optical fiber 34(see FIG. 2) or some other suitable source emits a combined opticalpower 960 that is received by a port 964. The latter can be any suitableelement such as, for example, a lens, an optical fiber interface orsimply an aperture such that the optical power is incident on photomixer908. In response to receiving the combined optical power, the photomixermixes the optical power to produce an emitted radiation such as, forexample, terahertz radiation. The emitted radiation propagates throughthe thickness of window 924 and is emitted into lens 934 such thatemitted radiation 968, shown as a dotted arrow, leaves lens 934 alonglight path 920′ based on prior adjustment of the position of lens 934.It is noted that emitted radiation 968 serves as a pre-sample radiationin FIG. 2.

Having described the operation of photomixing package or assemblyserving as a photomixing source, its operation as a photomixing detectorwill now be described with reference to FIG. 18 which is thediagrammatic, cut-away view, in elevation, of aforedescribed device 900or package of FIG. 17, but modified to show detection operation, forexample, with device 900 serving as detector 108 of FIG. 2. In thisconfiguration, a post-sample optical power 970 such as, for example,terahertz radiation that has passed through a sample a plurality oftimes, arrives at lens 934 along light path 920′ that is aligned withlight path 920 as a result of lens 934 being present in an adjustedposition. It is noted that that the presence of misalignment, as can beseen in prior art implementations described with regard to FIG. 1 b,wherein lens 934 is fixed in an incorrect, misaligned position, canresult in post-sample optical power 970 being misdirected to a direction974, represented by a dashed arrow at an angle with respect to lightpath 920′ that can cause the optical power to partially or completelymiss photomixer 908. Instead, lens 934 is positioned on window 924 tocompensate for such misalignment such that post-sample optical power 970is centered upon photomixer 908. At the same time, optical fiber 40 orsome other suitable source emits combined optical power 960 (see FIG. 2)that is received by port 964. In response to receiving the opticalpower, the photomixer mixes the combined optical power and post-sampleradiation 970 to produce an electrical output on pins 912 that isreceived by amplifier 120 of FIG. 2. In this way, the post-sampleelectromagnetic radiation is captured by the lens at an angularorientation that is adjustable responsive to sliding engagement of thelens on the window which changes the selective alignment and,thereafter, the optical power passes through the window to thesemiconductor device.

In view of FIGS. 17 and 18, it should be appreciated that lens 934 canbe selected, at least in part, based on the distribution at which thelens is desired to emit energy in FIG. 17 or to receive energy in FIG.18.

FIG. 19 is a diagrammatic plan view of a modified photomixing device orpackage, generally indicated by the reference number 900′ with theexception that lens 934 is supported for active movement against surface930 of the window (FIGS. 17 and 18) by an XY translational stage 1000.Accordingly, descriptions of like components will not be repeated forpurposes of brevity. The translational stage is supported by baseassembly 904 such that an X actuator 1004 engages periphery 939 of lens934 for bidirectional movement of the lens along one axis, asillustrated by a double-headed arrow 1008, and a Y actuator 1010 engagesperiphery 939 for independent bidirectional movement along another,orthogonal axis, as illustrated by a double-headed arrow 1014. Theactuators of the translation stage can utilize any suitable form ofmechanism for moving lens 934 including, but not limited to steppermotors, DC motors or piezoelectric elements. In this embodiment, aresilient member such as a spring or rubber gasket 1016 (FIGS. 17 and18) can provide a force that biases the lens against surface 930 of thewindow to maintain contact.

Referring to FIG. 17 in conjunction with FIG. 19, translational stage1000 permits adjustment of lens 934 such that light path 920′ can beselectively aligned with any one of a number of targets 1020 (some ofwhich are individually designated), arranged, for example, along an arc1024. Directed energy incident on the targets is diagrammaticallyillustrated by dashed arrows 1028. Of course, arc 1024 can be achievedusing a single actuator such that targets 1020 are in one plane. The useof XY translational stage 1000, however, allows for the distribution oftargets in three dimensions. The targets can be of any suitable typesuch that the directed energy can be collected from, including but notlimited to, free space, lenses, antennas and optical fibers.

Referring to FIG. 18 in conjunction with FIG. 19 in the context of adetection framework, translational stage 1000 permits adjustment of lens934 such that light path 920′ can be selectively aligned from any one ofa number of sources 1030 (some of which are individually designated),arranged, for example, along arc 1024. Source energy from the sources isdiagrammatically illustrated by dashed arrows 1034. As discussed above,arc 1024 can be achieved using a single actuator such that sources 1030are in one plane. The use of XY translational stage 1000, however,allows for the distribution of the sources in three dimensions. Thesources can be of any suitable type such that the source energy isreceivable by lens 934 including but not limited to free space, lenses,antennas and optical fibers.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form or formsdisclosed, and other modifications and variations may be possible inlight of the above teachings wherein those of skill in the art willrecognize certain modifications, permutations, additions andsub-combinations thereof.

What is claimed is:
 1. In a spectrometer including a source whichgenerates a source beam that includes electromagnetic radiation forcharacterizing a sample that is within a sample region, a sample cell,comprising: an annular support surrounding said sample region forreceiving the source beam along an entrance path such that the sourcebeam initially passes through the sample region and the sample containedin the sample region; and a set of reflectors supported by the annularsupport to define an optical path that reflects the source beam, afterinitially passing through the sample region, in a sequence ofalternating directions through the sample region at a plurality ofdifferent angles such that the source beam exits the set of reflectorsafter having passed through the sample region and any sample containedtherein a plurality of times.
 2. The sample cell of claim 1 wherein theelectromagnetic radiation is terahertz radiation.
 3. The sample cell ofclaim 1 wherein the source beam enters an aperture defined betweenadjacent ones of a plurality of reflectors that make up the set ofreflectors.
 4. The sample cell of claim 3 wherein the aforerecitedaperture is an entrance opening through which the source beam enters theset of reflectors and the source beam exits the set of reflectorsthrough an exit opening that is separate from the entrance opening afterpassing through the sample region a plurality of times.
 5. The samplecell of claim 3 wherein the aforerecited aperture is an opening throughwhich the source beam enters the set of reflectors and, thereafter, thesource beam emerges from the opening after passing through the sampleregion a plurality of times.
 6. The sample cell of claim 1 wherein theset of reflectors includes a plurality of mirrors and the mirrors arearranged in pairs on the optical path such that (i) a first mirror ofeach pair receives the source beam after the source beam passes throughthe sample region and reflects the source beam to a second mirror of thepair, and (ii) the second mirror of each pair reflects the source beamreceived from the first mirror back to the source region and cooperateswith the first mirror to focus the source beam into the sample region.7. The sample cell of claim 6 wherein at least one mirror of each pairof mirrors is a toroidal mirror to focus the source beam into the sampleregion.
 8. The sample cell of claim 1 wherein the set of reflectorsincludes a plurality of mirrors and the mirrors are arranged in pairs onthe optical path such that a first one of the mirrors of each pairreceives the source beam after passing through the source region and asecond one of the mirrors of each pair reflects the source beam receivedfrom the first mirror through the source region to a different, opposingpair of the mirrors on an opposite side of the annular support.
 9. Thesample cell of claim 1 wherein the optical path progresses stepwisearound the annular support.
 10. A spectrometer, comprising: a pluralityof the sample cells of claim 1 arranged in series such that the sourcebeam emerges from a first one of the sample cells and enters a secondone of the sample cells.
 11. A method for use in a spectrometerincluding a source which generates a source beam that includeselectromagnetic radiation for characterizing a sample that is within asample region, said method comprising: receiving the source beam alongan entrance path such that the source beam initially passes through thesample region and the sample contained in the sample region; anddefining an optical path that reflects the source beam, after initiallypassing through the sample region, in a sequence of alternatingdirections through the sample region at a plurality of different anglessuch that the source beam exits the set of reflectors after havingpassed through the sample region and any sample contained therein aplurality of times.
 12. In a spectrometer including a source whichgenerates a source beam that includes electromagnetic energy forcharacterizing a sample that is supported in a sample region, anapparatus, comprising: a micro-cell having an outer periphery includinga length extending between a first end and a second end such that aninterior portion of the micro-cell serves as said sample region, and themicro-cell defines a plurality of nano-pores for receiving the sample,each nano-pore having an elongated dimension extending at leastgenerally along a direction of said length and the nano-pores aredistributed along two orthogonal dimensions transverse to said length.13. The apparatus of claim 12 wherein the nano-pores include opposingpore ends that are sealed to contain the sample therein.
 14. Theapparatus of claim 12 wherein the nano-pores include opposing pore endsthat are open to support a flow of said sample therethrough.
 15. Theapparatus of claim 12 wherein the micro-cell is formed at least in partfrom at least one of a plurality of tubes and a plurality of rods thatare drawn to form the nano-pores.
 16. The apparatus of claim 12 whereinthe micro-cell is formed from at least one of plurality of tubes and aplurality of rods formed from at least one of fiberglass, carbon,polymer, plastic, quartz, silicon dioxide, silicon paraffin, biologicalmaterials and materials transparent to the electromagnetic energy. 17.The apparatus of claim 12 wherein the micro-cell includes a tubularshell which defines the outer periphery and which also defines aninterior cavity which receives a nano-fluidic cell that defines thenano-pores.
 18. The apparatus of claim 17 wherein the tubular shell isformed separately from the nano-fluidic cell.
 19. The apparatus of claim17 wherein the tubular shell is integrally formed with the nano-fluidiccell.
 20. The apparatus of claim 17 wherein the nano-fluidic cell isformed at least from a plurality of elongated cylindrical members thatdefine non-circular nano-pores therebetween.
 21. The apparatus of claim20 wherein the elongated cylindrical members are formed from at leastone of fiberglass, carbon, polymer, plastic, quartz, silicon dioxide,silicon paraffin, biological materials and materials transparent to theelectromagnetic energy.
 22. The apparatus of claim 17 wherein thenano-fluidic cell is formed at least from a plurality of bundledphotonic fibers with each photonic fiber defining at least some of thenano-pores.
 23. The apparatus of claim 12 wherein the outer peripherytransverse to said length forms a closed polygon having a plurality ofsides that are all adjoined by an obtuse angle.
 24. The apparatus ofclaim 12 wherein the outer periphery forms a plurality of facetsextending along said length.
 25. The apparatus of claim 24 wherein eachfacet is curved widthwise in the direction that is transverse to saidlength.
 26. The apparatus of claim 24 wherein each facet is convexwidthwise in the direction that is transverse to said length.
 27. Theapparatus of claim 24 wherein each facet is concave widthwise in thedirection that is transverse to said length.
 28. The apparatus of claim24 wherein each facet is linear widthwise in the direction that istransverse to said length.
 29. In a spectrometer including a sourcewhich generates a source beam that includes electromagnetic radiationfor characterizing a sample that is supported in a sample region, anapparatus, comprising: an annular support surrounding said sample regionfor receiving the source beam along an entrance path such the sourcebeam initially passes through the sample region and the sample containedin the sample region; a set of reflectors supported by the annularsupport to define an optical path that reflects the source beam, afterinitially passing through the sample region, in a sequence ofalternating directions through the sample region and at a plurality ofdifferent angles such that the source beam exits the set of reflectorsafter having passed through the sample region and any sample containedtherein a plurality of times; and a micro-cell supported within thesample region, said micro-cell having an outer periphery confronting theset of reflectors and the outer periphery includes a length extendingbetween a first end and a second end such that an interior portion ofthe sample cell serves as said sample region by receiving the samplewithin a plurality of nano-pores, each nano-pore having an elongateddimension extending at least generally along a direction of said lengthand the nano-pores are distributed along two orthogonal dimensionstransverse to said length.
 30. The apparatus of claim 29 wherein theelectromagnetic radiation is terahertz radiation.
 31. The apparatus ofclaim 29 wherein the source beam enters an aperture defined betweenadjacent ones of a plurality of reflectors that make up the set ofreflectors.
 32. The apparatus of claim 31 wherein the aforerecitedaperture is an entrance opening through which the source beam enters theset of reflectors and the source beam exits the set of reflectorsthrough an exit opening that is separate from the entrance opening afterpassing through the sample region a plurality of times.
 33. Theapparatus of claim 31 wherein the aforerecited aperture is an openingthrough which the source beam enters the set of reflectors and,thereafter, the source beam emerges from said opening after passingthrough the sample region a plurality of times.
 34. The apparatus ofclaim 29 wherein the set of reflectors includes a plurality of mirrorsand the mirrors are arranged in pairs on the optical path such that (i)a first mirror of each pair receives the source beam after the sourcebeam passes through the sample region and reflects the source beam to asecond mirror of the pair, and (ii) the second mirror of each pairreflects the source beam received from the first mirror back to thesource region and cooperates with the first mirror to focus the sourcebeam into the sample region.
 35. The apparatus of claim 33 wherein atleast one mirror of each pair of mirrors is a toroidal mirror to focusthe source beam into the sample region.
 36. The apparatus of claim 29wherein the set of reflectors includes a plurality of mirrors and themirrors are arranged in pairs on the optical path such that a first oneof the mirrors of each pair receives the source beam after passingthrough the source region and a second one of the mirrors of each pairreflects the source beam received from the first mirror through thesource region to a different, opposing pair of the mirrors on anopposite side of the annular support.
 37. The apparatus of claim 29wherein the optical path progresses stepwise around the annular support.38. The apparatus of claim 29 wherein the nano-pores include opposingpore ends that are sealed to contain the sample therein.
 39. Theapparatus of claim 29 wherein the nano-pores include opposing pore endsthat are open to support a flow of said sample therethrough.
 40. Theapparatus of claim 29 wherein the micro-cell is formed at least in partfrom a plurality of elongated cylindrical members that are drawn to formthe nano-pores.
 41. The apparatus of claim 40 wherein the elongatedcylindrical members are formed from at least one of fiberglass, carbon,polymer, plastic, quartz, paraffin and biological materials.
 42. Theapparatus of claim 29 wherein the micro-cell includes a tubular shellwhich defines the outer periphery and which also defines an interiorcavity which receives a nano-fluidic cell that defines the nano-pores.43. The apparatus of claim 42 wherein the tubular shell is formedseparately from the nano-fluidic cell.
 44. The apparatus of claim 42wherein the tubular shell is integrally formed with the nano-fluidiccell.
 45. The apparatus of claim 42 wherein the nano-fluidic cell isformed from a plurality of elongated cylindrical members.
 46. Theapparatus of claim 42 wherein the micro-cell is formed at least from aplurality of bundled photonic fibers with each photonic fiber definingat least some of the nano-pores.
 47. The apparatus of claim 29 whereinthe outer periphery transverse to said length forms a closed polygonhaving a plurality of sides that are adjoined by an obtuse angle. 48.The apparatus of claim 29 wherein the outer periphery forms a pluralityof facets extending along said length such that each facet includes amajor surface that is at least approximately centered on the opticalpath at least in the direction that is transverse to said length. 49.The apparatus of claim 48 wherein each facet is curved widthwise in thedirection that is transverse to said length.
 50. The apparatus of claim48 wherein each facet is convex widthwise in the direction that istransverse to said length.
 51. The apparatus of claim 48 wherein eachfacet is concave widthwise in the direction that is transverse to saidlength.
 52. The apparatus of claim 48 wherein each facet is linearwidthwise in the direction that is transverse to said length.